Aball is thrown at 25 m/s making an angle of 50° over a horizontal line. in which instant it velocity will make an 30° angle over a horizontal line?

0.68 sec

Explanation:

let the velocity be "v" when the angle is  30° .

Consider the motion along the horizontal direction

= initial velocity of ball along horizontal direction = 25 Cos50

= 16.07 m/s

= final velocity of ball along horizontal direction = v Cos30

we know that along the horizontal direction

=

v Cos30 = 16.07

v = 18.56 m/s

Consider the motion along the vertical direction

= initial velocity of ball along vertical direction = 25 Sin50

= 19.2 m/s

= final velocity of ball along vertical direction = v Sin30 = 25 Sin30 = 12.5 m/s

= acceleration = - 9.8 m/s²

= time taken

using the equation

12.5 = 19.2 + (- 9.8) t

t = 0.68 sec

b) phosphorus pentoxide

answer: the correct answer is 1.

explanation: there are various process in which a radioactive nuclei decays:

1) alpha decay: in this process, a heavier nuclei decays into lighter nuclei by releasing alpha particle. the mass number is reduced by 4 units.

2) electron capture: in this decay process, a parent nuclei absorbs an electron and gets converted into a neutron. simply, a proton and an electron combines together to form a neutron. mass number does not change in this process.

3) gamma ray emission: it is a decay process in which an unstable nuclei gives excess energy by a spontaneous electromagnetic process. this decay releases . this process does not change the mass number.

4) positron emission: it is a type of decay process, in which a proton gets converted to neutron and an electron neutrino. this is also known as -decay. in this the mass number remains same.

from the above information, we see that only alpha-decay is producing a change in the mass number of the nucleus.